Harvard Medical School Adviser by the Faculty of Harvard Medical School.

Q:

My doctor just diagnosed me with fatty liver disease. She says in my case it has nothing to do with drinking alcohol, which makes sense since I rarely drink. But I still don't understand it. Why do I have a problem that's usually caused by heavy drinking? She says it has to do with the fact that I've been overweight most of my life.

A:

Nonalcoholic fatty liver disease (NAFLD) was rarely diagnosed before 1980. But today, NAFLD is believed to affect as many as 30 percent of adult Americans.

NAFLD is actually not a single disease. Instead, it's a spectrum of disorders, all marked by the accumulation of fat inside liver cells. Under the microscope, this fatty buildup looks just like alcohol-induced fatty liver disease, but it occurs in people who consume little or no alcohol.

NAFLD usually causes no symptoms and few, if any, complications. However, some people with NAFLD go on to develop serious problems, which we'll discuss shortly.

The exact cause of NAFLD is unknown. But its emergence as a recognized and increasingly common disorder coincides with the epidemics of obesity and Type 2 diabetes. Both of these are associated with insulin resistance.

Obesity and insulin resistance, in turn, are implicated in "metabolic syndrome," a group of risk factors that increase the risk of cardiovascular disease, including a large waist and high triglycerides (a type of blood fat). Some experts consider NAFLD a symptom of metabolic syndrome.

The leading theory about NAFLD is that it's a result of metabolic changes driven by insulin resistance. More fat stays in the liver, accumulating in tiny sacs in the liver cells.

In its simplest form, NAFLD is just fat in the liver cells. This condition is called steatosis. While steatosis is not normal, it causes no symptoms and by itself is usually harmless. However, 5 percent to 20 percent of people with steatosis will develop a more serious form of NAFLD called nonalcoholic steatohepatitis, or NASH. In NASH, the fattened cells cause inflammation, swelling and cell death.

We don't know the cause of this more serious, inflammatory form of NAFLD or who is most likely to develop it, but it is not simply related to the amount of fat in the liver cells.

NASH is usually a relatively stable condition with few symptoms. Most people don't know they have it unless it shows up during a blood test or imaging procedure performed for other reasons. But unlike steatosis, NASH is not harmless.

In some people, it progresses slowly, over years to decades, sometimes causing vague complaints, such as fatigue, discomfort in the upper right abdomen or an overall sense of being unwell. Underlying these complaints may be a cascade of serious damage to the liver that culminates in massive scarring and impaired liver function called cirrhosis, the most advanced stage of NAFLD. Cirrhosis is irreversible and can lead to liver failure or cancer.

NASH is most closely associated with obesity, Type 2 diabetes and hyperlipidemia (high blood levels of triglycerides or cholesterol) -- conditions that, along with hypertension, constitute metabolic syndrome.

But not everyone with obesity, Type 2 diabetes and abnormal lipids has NASH. And some people with NASH have none of these risk factors. This suggests that genes and other factors play a role.

There's no cure for fatty liver disease or NASH. Treatment is aimed at reducing or preventing further fatty buildup and addressing underlying risk factors, such as obesity, diabetes and hyperlipidemia.

Lifestyle changes such as weight loss and a healthy diet can help. You may also want to talk to your doctor about medications to lower blood sugar and cholesterol and vitamin E supplements. Although there is some evidence that these measures may help, it's far too early to recommend any for routine treatment of fatty liver disease.

And perhaps it goes without saying, but to be clear on the issue of alcohol: People with NASH should not drink at all. And people with simple fatty liver -- that is, steatosis -- should at the very least minimize their alcohol consumption.

It also makes sense to avoid exposure to other liver toxins and to get immunizations against hepatitis B and A. But the most important measure of all is slow, steady weight loss -- and that requires a balanced, calorie-restricted diet along with regular exercise. It's another example of how healthful lifestyle choices actually improve health.

(Submit questions to harvard_adviser@hms.harvard.edu.)

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